Stacking devices for sheet articles



Aug. 3, 1965 c. FAREZ 3,198,513

STAGKING DEVICES FOR SHEET ARTICLES Filed June 28, 1963 2 Sheets-Sheet 1Q wag INVENTOR BY M ATTORNE E Aug. 3, 1965 c. FAREZ 3,198,513

STAGKING DEVICES FOR SHEET ARTICLES Filed June 28, 1963 2 Sheets-Sheet 2INVENTOR 00mm may BY ww w United States Patent C) 3,198,513 STACKMJGDEVICES 56R SHEET ARTLCLES Claude Farez, Saint Maui, France, assignor toQharvo, Grenoble (isere), France, a French joint-stock company Filedlune 28, 1963, Ser. No. 231,333 7 Claims. (Cl. 271-1) This inventionrelates to automatic stacking machines for flexible sheet'articles suchas hides or skins.

Hides or skins are frequently treated in a continuous process on endlessconveyors by being disposed on the conveyor at the inlet end thereof soas to pass through successive treating stations. At the outlet end ofthe conveyor the hides or skins are stacked either on a flat supportingtable or more generally on a pallet or horse and'it is frequentlyrequired that they be alternately disposed with the grain side up andwith the flesh side up, this being known as Marry stackingbecauseadjacent hides are in grain side to grain side or flesh side to fleshside contact. The automatic stacking device conveniently comprises amovable depositing member by means of which the successive hides orskins are fed so as to be properly positioned on the stack support.

A first diificulty to be solved in such stacking machines is that thehides or skins are disposed more or less at random at the inlet of theconveyor. It is therefore impossible to synchronize the operation of thedepositing member with the advance of the conveyor and some means mustbe devised to detect the arrival of the hides or skins at the outlet endof the conveyor and to time in correspondence the operation of thedepositing member. For instance the passage of each hide may be detectedby feelers disposed a short distance upstream of the outlet end of theconveyor (such conveyor being generally made of parallel strings orcables through which the feelers may project) and the depositing membermay begin to operate a pre-determined time after actuation of thefeelers by the incoming hide.

Another difiiculty encountered is that hides or skins are articles ofwidely varying shapes and dimensions. If therefore the detector meansand the delayed actuation of the depositing member have been so adjustedthat a hide of average shape and dimensions be properly disposed on thesupporting pallet with its center of gravity substantially inregistration with the midpoint or top line of the pallet, an abnormallylong or short hide will be liable to slip and to fall to the floor.

It has been proposed to separately detect the passage of the leadingedge and of the trailing edge of each hide and to operate the depositingmember in such a manner that a point situated midway between the leadingand the trailing edge be deposited on the midpoint of the support. Butthis solution would only be correct if the hides were in the form ofregular geometrical surfaces (as for instance of rectangles) and if theywere disposed on the conveyor with one of their axes parallel to thelongitudinal axis of the conveyor. Since these conditions are notfulfilled, the center of gravity of the hide may widely differ from themidpoint deduced from the leading and the trailing edge thereof andtherefore the stacking is not correctly effected.

It is an object of the present invention to provide a machine which willobviate these disadvantages and which will stack regularly sheetarticles such as hides or skins as they reach the outlet end of anendless conveyor irrespective of their varying shapes and/ ordimensions.

In accordance with the present invention in a machine for stackingflexible sheet articles of irregular shapes and dimensions which are fedby an endles conveyor of substantially transparent nature (as forinstance by an endless conveyor made of spaced parallel strings, cablesor the like), the article is caused to pass between a pair of ice to bestacked, and a pair of photo-electric cells respectively associated witheach surface, a signal is derived from the said cells when they receivethe same quantity of light, this meaning that the center of gravity ofthe article to be stacked is substantially situated on theabove-mentioned transverse line, and this signal is used to causedelayed operation of the movable depositing member.

. Of course in the absence of any article between the light-emittingsurfaces and the cells, the latter receive an equal quantity of lightand in autmatic operation without any attendant the device whichcompares the voltages received from the cells would emit a continuousspurious signal if no particular means were provided. Such means maypreferably consist of an auxiliary detector which only permit effectiveoperation of this comparing device when an article is present betweenthe light-emitting surfaces and the cells. This auxiliary detector maybe in the form of a narrow intermediate auxiliary light-emitting surfacedisposed between the above-mentioned or main lightemitting surfaces andassociated with an auxiliary cell. The voltage emitted by thi auxiliarycell may actuate a relay or the like which opens an appropriate electriccircuit to render the automatic comparing device ineffective as long asthe quantity of light received by the auxiliary cell exceeds apre-determined limit.

The movable depositing member is preferably in the form of areciprocating carriage disposed under the outlet end of the endlessconveyor (which will behereinafter designated as the main conveyor) andmovable substantially in parallel relation therewith, the said carriagesupporting an auxiliary conveyor which is permanently driven in thereverse direction with respect to the main conveyor and in such a mannerthat its absolute velocity, i.e. its velocity with respect to thestationary frame of the machine, remains always equal to the velocity ofthe main conveyor, irrespective of the displacements of the carriage.The carriage itself may be actuated in any appropriate manner, as forinstance by a double clutch with reversing gearing, by a reversibleelectric motor, by a pneumatic or hydraulic ram, etc.

In the annexed drawings:

FIG. 1 is a digrammatical side view illustrating the main constituentsof a stacking machine according to this invention.

FIG. 2 is a cross-section of a light-emitting surface with itsassociated parts.

FIG. 3 is a plan view showng a hide at its passage on the light-emittingsurfaces.

FIG. 4 is a general diagram of the electric circuits associated to thephoto-electric cells.

FIGS. 5 to 10 are simplified side views showing the successive steps ofa full operating cycle of the movable depositing carriage.

FIG. 11 is a diagrammatical perspective view illustrating a possibleembodiment of the carriage actuating mechanism.

FIG. 12 is a diagram of the electric circuits which con trol the doubleclutch of this mechanism.

FIG. 1 shows the outlet end of the endless conveyor 1 of a machine forthe treatment of sheet articles such as hides and skins, this conveyor(which will be hereinafter referred to as the rnain conveyor)beingformed of a large number of parallel endless strings or cablesstretched between end drums such as 2. Close below the effective upperrun of conveyor 1 and some what upstream of the end drum 2 are disposedthree light-emitting surfaces 3, 4 and 5'. Each surface such as 3comprises a fiat box 6 (FIG. 2) having a rectangular horizontal contourwith the inside painted in white, this box enclosing a number of tubularluminescent electric tubes 7 and being closed by a ground plate glass 8.These light-emitting surfaces extend transversely along the full widthof conveyor 1. Surfaces 3 and 5, which form the main light-emittingsurfaces of the machine, are disposed each side of surface 4 and theyextend longitudinally along a length at least equal to half the lengthof the longest hide which may have to be stacked, while surface 4, orauxiliary light-emitting surface, is quite narrow, its dimension in thelongitudinal irection of conveyor 1 being negligible with respect tosurfaces 3 and 5. A photo-electric cell is associated to each main orauxiliary light-emitting surface, these cells, referenced respectively66, 6'7 and 68, being disposed above conveyor 1, each at the top of alight collecting hood 9, 1G and 11.

When no hide is present between the light emitting surfaces 3, 4, andthe corresponding cells 66, 67, and 68, the main cells 66 and 68 (i.e.those corresponding to the main light-emitting surfaces 3 and 5) areequally illuminated and the auxiliary cell 67 (corresponding to theauxiliary light-emitting surface 4) is fully illuminated. When a hidesuch as 12 (FIG. 3) passes on the lightemitting surfaces it succesisvelyinfluences cells 66, 67 and 63 by reducing the quantity or intensity oflight received by each cell. When the hide is simultaneously on bothmain surfaces 3 and 5 (as illustrated in FIG. 3) the light received bycell 66 increases progressively (since the hide is leaving surface 3),while the light received by cell 68 decreases progressively (the hidecoming on surface 5). When both cells are equally illuminated the areaof the portion of the hide which covers surface 3 is exactly equal tothe portion thereof which covers surface 5, which means that the centerof gravity of the hide, considered as a mere geometrical surface, isexactly situated on the transverse line of symmetry of the illuminatingunit, as indicated at G, the influence of the quite narrow intermediateauxiliary surface 4 being negligible. It may besides be remarked that ifthe portion of the hide which covers surface 4 is substantiallyrectangular, the presence of this auxiliary surface has no influencewhatever on the position of point G. 7 Now a hide is generally ofsubstantially uniform thickness and density, and therefore its center ofgravity fairly corresponds with the center of gravity of its contourconsidered as a geometrical surface.

It results from the above description that the passage of the center ofgravity of the hide across the transverse axis of symmetry of theilluminating unit may be detected by the equality of the voltagesemitted by the main cells 66 and 68, and by a simultaneous substantialreduction of the voltage from the auxiliary cell 67.

FIG. 4 illustrates an arrangement of electric circuits whereby a signalmay be derived from the above operation of cells 66-68. The main cells66 and 68 act in one and the other direction on an amplifier 13 whichemits a resultant outlet voltage proportional to the difference be tweenthe inlet voltages received from cells 66 and 68. This resultant voltageis applied to a polarized relay or galvanometer 14 the movable member 15of which forms a contact cooperating with two fixed contacts 16connected with the coil of a relay 17 having its contacts normallyclosed. This relay is inserted in an electric line 18 which is connectedwith a registering device or memory 19. In line 18 is inserted anotherrelay 20 the coil of which is energized by the auxiliary cell 67. Thisrelay is also of the type having its contacts normally closed and it isfurther so arranged that it is only actuated (i.e. that its contacts areonly open) when cell 67 is almost fully illuminated. This may beobtained in any appopriate manner, as for instance by properly adpustingits biassing spring, or by inserting a Zener diode in series with itscoil.

In the absence of any hide between the auxiliary lightemitting surface 4and the auxiliary cell 67, the latter is fully illuminated, relay 20 istherefore open and no voltage movable member or contact 15 is at theneutral position between contacts 16. Relay 17 is unenergized and its.

contacts are closed. When the leading edge of an incoming hide such as12 (FIG. 3) reaches the first main light-emitting surface 3, the maincells 66 and 63 are no more equally illuminated, the movable contact 15deviates and engages one of the fixed contacts 16 so that relay 17 isenergized and that it opens its contacts. When the leading edge of hide12 reaches the auxiliary surface 4, the voltage emitted by the auxiliarycell 67 is substantially reduced and therefore relay 2t) closes itscontacts, but memory 19 cannot receive any current from line 18 sincethe contacts of relay 17 are open. But when the center of gravity G ofhide 12 passes across the transverse line of symmetry of theilluminating unit the voltages emitted by the main cells 66 and 68 aremomentarily equal, the movable contact 15 of galvanometer 14 returns toits neutral position (or more exactly it moves from one fixed contact 16to the other one and therefore passes through the neutral position) andrelay 17 being unenergized, its contacts close for a short time. Memory19 thus receives a current pulse. This memory is so arranged as to starta movable depositing carriage, still to be described, a predeterminedtime after it has received such a pulse.

The horizontally movable depositing carriage 21 is disposed immediatelybelow the outlet end of conveyor 1, this carriage being guided byappropriate guides, not illustrated. Carriage 21 supports an auxiliaryconveyor 22 which may be formed, as the main conveyor 1, of a number ofparallel strings stretched between end drums 23 and 24, though it may beof any appropriate form. The end drum 23 which. is upstream with respectto the main conveyor 1 (i.e. the left-hand end drum in FIG. 1) has alateral sprocket 25 which cooperates with an endless chain 26 whichpasses on a sprocket 27 carried by the corresponding end of the end drum2 of the main conveyor 1, on a returning sprocket 28 supported .by theframe of the machine (not illustrated) and finally on a second returningsprocket 29 supported by carriage 21 itself. Sprockets 25 and 27 havethe same number of teeth and of course the same diameter.

It will be understood that assuming that carriage 21 is at a standstill,the sprocket 25 of the end drum 23 of the auxiliary conveyor 22 rotatesat the same speed as the sprocket 27 of the end drum 2 of the mainconveyor 1. If both end drums 2 and 23 have the same diameter, thelinear velocity of the auxiliary conveyor 22 will be exactly equal tothat of the main conveyor 1, but in the reverse direction. Alternativelysprockets 25 and 27 could have different number of teeth provided theratio of the numbers of drums 23 and 2 be equal to the ratio of thesediameters. When carriage 21 moves, this equality of the linearvelocities of conveyors 22 and 1 is not perturbed provided the velocityof conveyor 22 is considered with respect to the stationary frame of themachine (absolute velocity) and not with respect to the movable frame ofthe carriage (relative velocity). It is clear for instance that ifconveyor 1 is at standstill (velocity Zero), the absolute velocity ofconveyor 22 will be zero whatever may be the movement of the carriage.

It is now possible to describe the general operation of the stackingmachine before going into the details of its controlling and actuatingdevices.

The beginning of an operating cycle may for instance correspond to theposition diagrammatically illustrated in FIG. 5. The depositing carriageis at standstill at the right-hand end of its stroke with itsleft-handend drum 23 slightly upstream of the end drum 2 of the mainconveyor 1 (the term upstream being used here with reference to the mainconveyor). The stacking pallet or horse 30 is in position to receive thehides in flesh side to flesh side contact. In practice this pallet ismounted on a wheeled carriage and its proper position is carefullyindicated on the floor or is determined by positive positioning meanssuch as lateral guides and transverse abutments.

When a hide 12 reaches the outlet end of the main conveyor 1, it passeson the auxiliary conveyor 22 which moves it towards the left (i.e.upstream with respect to the main conveyor) until it hangs verticallyfrom the lefthand end drum 23, as shown. At an appropriate time carriage21 is started by the above-described memory ll? of PEG. 4 to effect itsstroke towards the left and the hide is progressively deposited on horse36 as indicated in FIG. 6. It is to be observed that the regulartransfer of the hide 12 from the main conveyor 1 onto the auxiliaryconveyor 22 is only possible because the absolute velocities of bothconveyors are equal. Further the advancing speed of the depositingcarriage 21 should be lower than the absolute velocities of bothconveyors, since otherwise the relative velocity of the auxiliaryconveyor 22 with respect to its supporting carriage 21 would'be negative(i.e. directed towards the right) and the hide would hang and fall fromend drum 24.

It is to be noted that the side of the hide which rests on the stackinghorse 3% is the same as that which was on the main conveyor 1. In otherwords the hide has not been inverted.

When the hide has thus been deposited, carriage 21 continues its strokeand stops at the position shown in FIG. 7, for which its right-hand enddrum 24 is just slightly downstream of the end drum 2 of the mainconveyor (the term downstream being here again used with reference tothe main conveyor).

When another hide 12' reaches the outlet end of the main conveyor 1, itis again transferred onto the auxiliary conveyor 22 on which it movesupstream with respect to the main conveyor 1, i.e. towards the left, asillustrated in FIG. 7. The hide 12' therefore reaches end drum 23 and ithangs therefrom as indicated in FIG. 8. The carriage is then againstarted by the memory 19 to effect its stroke towards the right and thehide is regularly deposited on the horse or pallet 39, as indicated inFIG. 9. The depositing carriage stops when it reaches its initialposition, as indicated in FIG. (which is to be compared with PEG. 5).The side of hide 12 which rests on horse (or more exactly on thepreviously stacked hide 12) is the side which was facing upwardly on themain conveyor 1. In other words the hide 12 has been inverted and thesuccessive hides will be stacked in grain to grain and flesh to fleshcontact.

It is further to be noted that proper operation requires that thedepositing carriage 21 moves at a sufficiently high speed sinceotherwise the hide would fall from the end drum 23 before reaching thestacking horse 3d. Carriage 21 should therefore be driven alternately ata low speed towardsthe left and at a high speed towards the right.

FIG. 11 diagrammatically illustrates a possible driving mechanism forthis purpose. A shaft 31 is connected in any appropriate manner with themain conveyor 1 or with the driving gearing thereof. Shaft 31 has abevel pinion 32 which meshes with two opposed bevel gears 33 and 34carried by alined shafts 35 and 36. On each shaft 35 or 36 is mounted asprocket wheel, respectively 37, 33, connected by a chain 39, 4% withanother sprocket wheel 40, 41, wheels 44 and 41 being loosely mounted ona common shaft 43. Shaft 43 supports a double clutch 44, as for instanceof the electromagnetic type, by means of which wheels 4t) and 41 may beselectively coupled with shaft 43. Shaft 43 has a pinion 45 which mesheswith a rack 46 carried by the depositing carriage 21.

It will be apparent that the double clutch 44 permits to drive carriage21 in one or the other direction at two different speeds, as determinedby the relative diameters of sprockets 37-41 and 38-42.

FIG. 12 shows an embodiment of a device to control operation of carriage21. The memory 19 of FIG. 4 has been illustrated as in the form of anendless member capable of registering signals emitted by the relay 17 ofFIG. 4. Memory 19 may for instance be formed ofa drum carrying anannular row of needles which are frictionally slida ole in longitudinalholes of the drum. This form of mechanical memory being conventional inthe art, it has not been described nor illustrated in greater details.In FIG. 12 reference numeral 19 may be considered as designating aportion of the drum, the needles being not illustrated. Referencenumeral 43 indicates the solenoid which pushes the needleslongitudinally with respect to the drum (i.e. downwardly in FIG. 12)under control of relay 17 of FIG. 4 so as to register in the memory(i.e. on the drum) the pulses received from the said relay. Referencenumerals 49 and 5t designate two successive needle feeler switchesrespectively corresponding to the upstream and to the downstream strokeof carriage 21 (upstream and downstream referring to the movement of themain conveyor 1). Each feeler switch closes an electromagnetic switch orcontactor switch, respectively 51, 52, which in turn controls one ofthecircuits of the double clutch 44. In order to avoid that bothcircuits of clutch 44 be simultaneously energized, each contactor switchcomprises an auxiliary contact 53, 54 inserted in the actuating circuitof the other contactor switch so as only tobe closed when the firstcontactor switch is open, in such a manner that when once a contactorswitch such as 5'1 is closed, the other one 52 cannot be closed beforethe first one has returned to the open position. \Contactor switches 51and 52 are'of the self-retaining type and in their retaining circuit 55,respectively 56, is inserted a normally closed end switch 57, 58actuated by carriage 21 when same reaches the end of one of its strokes.

' There is further provided a restoring device 59 (such as a stationarycam surface) which returns the needles of the memory drum 1-9 to theirinoperative position.

Drum 1-9 may be rotated in any appropriate manner, as for instance by aseparate constant speed motor, but it is preferable'to derive its drivefrom the machine it self, as for instance from the end drum 2 of themain convey-or l, in order that its rotational speed be alwaysproportional to the linear speed of the conveyors.

Supposing that the depositing carriage 21 is at its lefthand end stroke,it maintains switch 57 at the open position and therefore feeler switch49 cannot close con.- tactor switch '51. When a hide passes on theilluminating unit, relay 17 of FIG. 4 registers its passage in memory 19by causing solenoid 48 to displace one or several suc cessive needlesthereof. These needles thereafter actuate feeler switch 49 but, as aboveexplained, this actuation has no elfect on contactor switch 51, switch57 being open. But when the first needle displaced by solenoid 48reaches feeler switch 5%, the latter close contactor switch 52 which inturn actuates the double clutch 44 in such a manner as to displacecarriage 21 towards the right at the proper speed. At the end of itsstroke carriage 21 opens switch 56 and therefore returns contactorswitch 52 to the open position. When the passage of the next hide isregistered in memory 19, switch 57 will be closed and switch 53 will beopen. Fee er switch 49 will therefore be effective while feeler switch5% will be inetfective. When the first needle displaced by solenoid 48reaches feeler switch 49, the latter will close contactor switch 51 andcarriage 21 will move towards the left until it opens switch 57 at theend of its stroke.

It will be observed that the time elapsed between passage of the centerof gravity of the hide on the illuminating unit, as indicated in FIG. 4,and the starting of the depositing carriage 21 may be adjusted at willfor each stroke of the carriage by merely displacing feeler switches 49and/or 50 with respect to the memory drum or carrier 19. Thedisplacements of the carriage may thus be so timed that the center ofgravity of the hide be always disposedon the top of horse or pallet sowhatever may be the shape or dimensions of the hide since the signalregistered in memory 19 corresponds to passage of the center of gravityof the hide across a fixed transverse line of the frame.

It will be observed that the device of FIG. 12 may operate with any kindof memory and with any kind of carriage driving gear, the double clutchof FIG. 11 being only illustrative of one of the many possibilities ofthe present invention.

For instance the driving shaft 43 of FIG. 11 could be connected bygears, pulleys or otherwise with a reversible two speed electric motor,contactor switches 51 and 52 being so arranged as to actuate this motorrespectively in one direction at a first speed and in the reversedirection at the other speed.

The pinion-and-rack gearing 4546 of FIG. 11 could be replaced by a drumon which would be wound in one and the other direction the ends of anendless cable, belt or like flexible member attached to the carriage andappropriately guided by idle pulleys. Alternatively the carriage couldbe attached to an endless belt stretched between two end pulleys, one ofthe latter being driven by a reversible two-speed motor, or by a doubleclutch such as clutch 44 of FIG. 11.

In another embodiment the depositing carriage 21 could be reciprocatedby a pneumatic or hydraulic ram to the ends of which fluid underpressure would be supplied through two electromagnetic valves controlledby contactor switches 51 and 52 of FIG. 12. The advancing speed could beadjusted by pressure regulators or throttling members respectivelyassociated with each valve. 'Each valve would be double in order thatwhen actuated it would inject fluid under pressure into one end of theram and at the same time connect the other end with an exhaust line.

I claim:

1. A machine for stacking opaque flexible sheet articles, such as hidesand skins, comprising a main endless conveyor with a substantially flatarticle-carrying portion having a first side and a second side and anoutlet end, and being at least in part transparent to light in thevicinity of said outlet end, said articles being disposed at random onone of said first and second sides of said article-carrying portion ofsaid main conveyor to be carried thereby towards said outlet end at agiven linear speed; two stationary main lightemitting surfaces disposedon the first side of said article-carrying portion of said main conveyorin the vicinity of the outlet end thereof and extending across the fullwidth thereof substantially symmetrically with respect to a linetransverse to said article-carrying portion of said main conveyor andclose to said line so as to illuminate the articles carried by same,said surfaces having a substantially uniformly distributed luminosityand said surfaces each having a dimension longitudinally of saidarticle-carrying portion of said main conveyor at least equal to halfthe maximum length of the articles to be stacked; two main photoelectriccells disposed on the second side of said articlecarrying portion ofsaid main conveyor, each to receive light substantially from one only ofsaid main lightemitting surfaces; comparing means to compare thevoltages emitted by said main photo-electric cells and to deduce fromsuch comparison the passage across said transverse line of theapproximate center of the surface of an article carried by said mainarticle-carrying portion of said main conveyor between said mainlight-emitting surfaces and said cells; a stacking support disposed inthe vicinity of the outlet end of said article-carrying portion of saidmain conveyor and on which the articles carried by said conveyor are tobe stacked; depositing means to receive the articles from the outlet endof said articlecarrying portion of said main conveyor and to depositsame on said support; driving means to drive said depositing means; andmeans to actuate said driving means a pre-determined time after saidcomparing means have detected passage of the approximate center of thesurface {3 0 of an article across said transverse line to. substantiallyregularly stack same on said support.

2. In a machine as claimed in claim 1, means to detect the presence ofan article between said main lightemitting surfaces and said mainphoto-electric cells to avoid spurious operation of said depositingmeans under the action of said comparing means in the absence of anyarticle on said article-carrying portion of said main conveyor betweensaid main light-emitting surfaces and said main photo-electric cells.

3. In a machine as claimed in claim 1, an auxiliary lightemittingsurface disposed between said main lightemitting surfaces, saidauxiliary surface extending substantially across the full width of saidarticle-carrying portion of said main conveyor and being of smalldimension with respectto said main surfaces longitudinally of said mainconveyor, and said auxiliary surface being disposed on one of said firstand second sides of said article-carrying portion of said main conveyor;an auxiliary photo-electric cell disposed on the other side of saidarticle-carrying portion of said conveyor to receive light substantiallyexclusively from said auxiliary lightemitting surface; and means undercontrol of voltage from said auxiliary photo-electric cell to preventsaid driving means from being actuated when the voltage from saidauxiliary cell exceeds a pre-determined limit.

4. In a machine as claimed in claim 1, said depositing means comprisinga carriage reciprocatable under said article-carrying portion of saidmain conveyor in the vicinity of the outlet end thereof andsubstantially in parallel relation thereto; an auxiliary endlessconveyor supported by said carriage; and means to move said auxiliaryconveyor at an absolute linear speed equal to the linear speed of saidarticle-carrying portion of said main conveyor and in the reversedirection with respect thereto independently of the movement of saidcarriage.

5. A machine for stacking opaque flexible articles such as hides andskins, comprising a main endless conveyor with an article-carryingportion having an outlet end, said articles being disposed at random onsaid articlecarrying portion of said conveyor to be carried thereby at agiven linear speed; a depositing carriage reciprocatable under saidarticle-carrying portion of said main conveyor in the vicinity of theoutlet end thereof and in substantially parallel relation thereto; anauxiliary endless conveyor supported by said carriage, said auxiliaryconveyor also having an article-carrying portion; means to move saidarticle-carrying portion of said auxiliary conveyor at an absolutelinear speed equal to the linear speed of said article-carrying portionof said main conveyor and in the reverse direction with respect theretoindependently of the movement of said carriage; first carriage drivingmeans to cause said depositing carriage to effect a first stroke in thereverse direction with respect to the movement of said article-carryingportion of said main conveyor at a speed lower than the linear speedthereof; second carriage driving means to cause asid depositing carriageto effect a second stroke in the same direction as the movement of saidarticle-carrying portion of said main conveyor at a speed higher thanthe linear speed thereof; means to detect the passage of the approximatecenter of the surface of an article across a line transverse to saidarticle-carrying portion of said main conveyor and situated at adistance upstream of the outlet end thereof; and means to alternatelyactuate said first carriage driving means and said second carriagedriving means a pre-determined time after passage of the approximatecenter of the surface of an article across said line.

6. An apparatus to detect the passage of the approximate center of thesurface of an opaque flexible sheet article moving across asubstantially linear path across a stationary line transverse to saidpath, comprising two stationary main light-emitting surfaces disposed ona first side of said path, symmetrically with respect to said line andclose to same, and extending across the full width of said path in suchmanner that said article fully passes in front of them, each of saidsurfaces having a dimension longitudinally of said path at least equalto half the length of said article, and said surfaces further having asubstantially uniformly distributed luminosity; two photo-electric cellsdisposed on the second side of said path each to receive light from oneonly of said light-emitting surfaces; and means to compare the voltagesfrom said cells during passage of said articles in front of saidlight-emitting surfaces.

7. A method to detect the passage of the approximate center of thesurface of a moving opaque flexible sheet article across a linetransverse to the path thereof which comprises, the steps of passing asheet article in front of two spaced light-emitting surfaces bothlocated on one side of said sheet article; detecting the light emittedby each of said light-emitting surfaces which pass to the other side ofsaid sheet article; comparing the light emit- -10 ted which passes tothe other side from one light-emitting surface wtih the light emittedwhich passes to the other side from the other light-emitting surface;and ascertaining the moment when the light emitted which passes to theother side from both surfaces are the same.

References Cited by the Examiner UNITED STATES PATENTS HENSON WOOD, JR.,Primary Examiner.

ROBERT B. REEVES, Examiner.

1. A MACHINE FOR STACKING OPAQUE FLEXIBLE SHEET ARTICLES, SUCH AS HIDESAND SKINS, COMPRISING A MAIN ENDLESS CONVEYOR WITH A SUBSTANTIALLY FLATARTICLE-CARRYING PORTION HAVING A FIRST SIDE AND A SECOND SIDE AND ANOUTLET END, AND BEING AT LEAST IN PART TRANSPARENT TO LIGHT IN THEVICINITY OF SAID OUTLET END, SAID ARTICLES BEING DISPOSED AT RANDOM ONONE OF SAID FIRST AND SECOND SIDES OF SAID ARTICLE-CARRYING PORTION OFSAID MAIN CONVEYOR TO BE CARRIED THEREBY TOWARDS SAID OUTLET END AT AGIVEN LINEAR SPEED; TWO STATIONARY MAIN LIGHT-EMITTING SURFACES DISPOSEDON THE FIRST SIDE OF SAID ARTICLE-CARRYING PORTION OF SAID MAIN CONVEYORIN THE VICINITY OF THE OUTLET END THEREOF AND EXTENDING ACROSS THE FULLWIDTH THEREOF SUBSTANTIALLY SYMMETRICALLY WITH RESPECT TO A LINETRANSVERSE TO SAID ARTICLE-CARRYING PORTION OF SAID MAIN CONVEYOR ANDCLOSE TO SAID LINE SO AS TO ILLUMINATE THE ARTICLES CARRIED BY SAME,SAID SURFACES HAVING A SUBSTANTIALLY UNIFORMLY DISTRIBUTED LUMINOSITYAND SAID SURFACES EACH HAVING A DIMENSION LONGITUDINALLY OF SAIDARTICLE-CARRYING PORTION OF SAID MAIN CONVEYOR AT LEAST EQUAL TO HALFTHE MAXIMUM LENGTH OF THE ARTICLES TO BE STACKED; TWO MAIN PHOTOELECTRICCELLS DISPOSED ON THE SECOND SIDE OF SAID ARTICLECARRYING PORTION OFSAID MAIN CONVEYOR, EACH TO RECEIVE LIGHT SUBSTANTIALLY FROM ONE ONLY OFSAID MAIN LIGHTEMITTING SURFACES; COMPARING MEANS TO COMPARE THEVOLTAGES EMITTED BY SAID MAIN PHOTO-ELECTRIC CELLS AND TO DEDUCE FROMSUCH COMPARISON THE PASSAGE ACROSS SAID TRANSVERSE LINE OF THEAPPROXIMATE CENTER OF THE SURFACE OF AN ARTICLE CARRIED BY SAID MAINARTICLE-CARRYING PORTION OF SAID MAIN CONVEYOR BETWEEN SAID MAINLIGHT-EMITTING SURFACES AND SAID CELLS; A STACKING SUPPORT DISPOSED INTHE VICINITY OF THE OUTLET END OF SAID ARTICLE-CARRYING PORTION OF SAIDMAIN CONVEYOR AND ON WHICH THE ARTICLES CARRIED BY SAID CONVEYOR ARE TOBE STACKED; DEPOSITING MEANS TO RECEIVE THE ARTICLES FROM THE OUTLET ENDOF SAID ARTICLECARRYING PORTION OF SAID MAIN CONVEYOR AND TO DEPOSITSAME ON SAID SUPPORT; DRIVING MEANS TO DRIVE SAID DEPOSITING MEANS; ANDMEANS TO ACTUATE SAID DRIVING MEANS A PRE-DETERMINED TIME AFTER SAIDCOMPARING MEANS HAVE DETECTED PASSAGE OF THE APPROXIMATE CENTER OF THESURFACE OF AN ARTICLE ACROSS SAID TRANSVERSE LINE TO SUBSTANTIALLYREGULARLY STACK SAME ON SAID SUPPORT.